How do you build a cloud API security strategy that works?

A cloud API security strategy is a ranked set of controls across the API life cycle: know every API you run, check authorization on every object, limit resource use, and treat third party APIs as untrusted. Start with inventory and authorization, because most API incidents come from missing checks, not exotic exploits.

What does the risk list say?

The OWASP API Security Top 10 for 2023 is the clearest map. Its ten items include broken object level authorization, broken authentication, broken object property level authorization, unrestricted resource consumption, broken function level authorization, unrestricted access to sensitive business flows, server side request forgery, security misconfiguration, improper inventory management and unsafe consumption of APIs.

Read the list as a strategy outline rather than a checklist. Four of the ten are about who may do what (items 1, 2, 3 and 5). Two are about volume and abuse (4 and 6). The rest are about what you expose, how you configure it and what you trust.

NIST also publishes guidance for API protection in cloud-native systems as SP 800-228. NIST's page notes the June 2025 text was withdrawn on 13 March 2026 and superseded by a newer version, so use the current one from the NIST site rather than a saved copy. Its abstract describes recommended basic and advanced controls for the pre-runtime and runtime stages and an incremental, risk based approach.

Where do you start?

Order matters. A reasonable sequence:

1. Inventory. OWASP's improper inventory management item notes APIs expose more endpoints than a typical web app, so documentation and an up to date list of hosts and versions are essential. Old versions and debug endpoints are what people forget.
2. Authorization at the object level. Every function that takes an identifier from the user must check that this user may touch this object.
3. Authentication for the clients you have. Weak token handling undermines everything above.
4. Limits. Bandwidth, CPU, memory, and also paid downstream calls such as SMS or email, which OWASP notes can raise costs as well as cause outages.
5. Outbound controls. SSRF happens when your API fetches a URL a caller supplied. OWASP notes it can succeed even behind a firewall or VPN.

What does a real gap look like?

Constructed example: a retail orders API has an endpoint to fetch an order by number. A signed in customer changes the number in the request and receives another customer's order. The gateway authenticated the caller, the schema validated the format, and the WAF saw nothing odd. The fault sits in the handler, which never asked whether the order belongs to the caller. That is the object level authorization failure OWASP ranks first, and only a test or a code review finds it.

A second example: a partner API your service calls returns a field you copy into a database query without validation. OWASP's tenth item says developers tend to trust third party data more than user input, so attackers go after the integration.

Which controls belong where?

Put the generic controls at the edge: TLS, rate limits, schema checks, token validation, a gateway. Put the business controls in the service: who owns this record, which roles may call this function, which flows need extra friction. A gateway cannot know that order 1042 belongs to someone else. Do not let edge controls give a false sense that service checks are optional.

How to check or apply this

1. Build the inventory from several sources: gateway config, cloud load balancers, code, and traffic logs. Compare them.
2. Retire or lock down every version and endpoint with no owner.
3. Write authorization tests that call each endpoint as a different user and expect denial.
4. Set per client and per function limits, including on costly downstream calls.
5. Validate and constrain any URL your service will fetch, with an allow list.
6. Log enough to answer who called what, and alert on enumeration patterns.

Quick check

Sources

• OWASP Top 10 API Security Risks, 2023
• NIST SP 800-228, Guidelines for API Protection for Cloud-Native Systems

Last reviewed: 18 October 2026.